Method and system for adaptive interleaving

ABSTRACT

A method a system for automatically controlling an adaptive interleaver involves monitoring performance parameters of a transmission system and controlling the adaptive interleaver in response to the performance parameters. The SNR and the data rate of the transmission system are preferably determined. The data rate is analyzed and the adaptive interleaver is adjusted in response to the data rate and the SNR. Alternatively, the BER and the data rate of the transmission system are determined. The data rate is analyzed and the adaptive interleaver is adjusted in response to the data rate and the BER. Alternatively, any one of the SNR, BER or data rate can alone be monitored and used to the adaptive interleaver. The system provides a effective system for adjusting an adaptive interleaver in response to performance parameters of a transmission system.

BACKGROUND

The present invention relates generally to transmission systems and morespecifically to adaptive interleavers.

Interleaving is a coding technique that is commonly used to increase theperformance of transmission systems by decreasing errors in the system.Interleaving rearranges the data that is to be transmitted in a giventransmission thereby improving the error-correction performance ofredundancy coding techniques. Interleaving increases the transmissionlatency of the interleaved transmissions. Latency is the time requiredfor data to traverse the end-to-end transmission path.

In most applications, the latency associated with interleaving is only asmall portion of the overall latency of the system. However, intelecommunications applications, and particularly with reference todigital subscriber lines, the latency associated with interleavingconstitutes a significant portion of the overall latency. High latencycan have a substantial negative impact on system performance especiallywhen the system is operating at high data transmission rates. The impactis especially pronounced for systems where many end-to-end transmissionsare required to accomplish a task, such as systems utilizing the popularTCP/IP data communications protocol to send a large file. Accordingly,telecommunications system providers generally strive to minimize latencythroughout their systems while still utilizing interleaving to offsetthe adverse effects of errors. Thus, it is desirable to optimize theinterleaving used such that only the degree of interleaving necessary toachieve a desired performance level is implemented.

Adaptive interleaving allows for different degrees of interleaving,commonly referred to as the interleave depth, to be applied to differenttransmissions. Adaptive interleavers are known to those skilled in theart. U.S. Pat. No. 4,901,319 describes an adaptive interleave system,including an adaptive interleaver, that attempts to correct errors thatoccur as a result of the fading characteristics of a radio channel. Thesystem measures the phase error of transmissions in an effort toidentify errors in the transmissions. The system utilizes a complexsystem and method to predict the next error occurrence based upon themeasured phase error, and adjusts the adaptive interleaver in responseto the prediction. However, measuring the phase error is not aneffective method for identifying errors in many transmission systems.Also, a complex system for predicting the occurrence of errors andcontrolling an adaptive interleaver can be difficult to implement onmany transmission systems.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of the adaptive interleaver controller of afirst preferred embodiment.

FIG. 2 is a more detailed block diagram of the adaptive interleavercontroller of FIG. 1.

FIG. 3 is a more detailed block diagram of the adaptive interleavercontroller of FIG. 1

FIG. 4 is a more detailed block diagram of the adaptive interleavercontroller of FIG. 1

FIG. 5 is a more detailed block diagram of the adaptive interleavercontroller of FIG. 1

FIG. 6 is a more detailed block diagram of the adaptive interleavercontroller of FIG. 1

FIG. 7 is a flow chart of a method for controlling an adaptiveinterleaver of a first preferred embodiment.

FIG. 8 is a flow chart of a method for controlling an adaptiveinterleaver of a second preferred embodiment.

FIG. 9. is a flow chart of a method for controlling an adaptiveinterleaver of a third preferred embodiment.

FIG. 10. is a flow chart of a method for controlling an adaptiveinterleaver of a fourth preferred embodiment.

FIG. 11 is a flow chart of a method for controlling an adaptiveinterleaver of a fifth preferred embodiment.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

The present embodiments provide an effective system for automaticallycontrolling an adaptive interleaver in response to the performanceparameters of a transmission system. Referring now to FIG. 1, acontroller 5 for determining one or more performance parameters andgenerating an adaptive interleave control signal in response to theperformance parameters is shown. The controller 5 preferably comprisesmeans 1 for analyzing input signals, means 2 for providing an adaptiveinterleave control signal, means 3 for determining a first performanceparameter and means 4 for determining a second performance parameter.The means 3 for determining a first performance parameter preferablycomprises a first performance parameter monitor for determining a firstperformance parameter and generating a first input signal as known tothose skilled in the art. The means 4 for determining a secondperformance parameter preferably comprises a second performanceparameter monitor for determining a second performance parameter andgenerating a second input signal as known to those skilled in the art.The performance parameters are preferably chosen from the groupconsisting of signal to noise ratio (SNR), bit error rate (BER) and datarate.

As illustrated in the following embodiments, the system preferablydetermines the SNR and the data rate of the transmission system. Thedata rate of the system is analyzed and the adaptive interleaver isadjusted in response to the data rate and the SNR. Alternatively, thebit error rate (BER) and the data rate of the transmission system can bedetermined. The data rate of the system is analyzed and the adaptiveinterleaver is adjusted in response to the data rate and the BER.Alternatively, any one of the SNR, BER or data rate can alone bedetermined and used to control the adaptive interleaver. While such asystem is of particular importance with regard to digital subscriberlines, those skilled in the art will appreciate that it is applicable toany system that incorporates interleaving.

By way of example, FIG. 2 shows a transmission system 10 comprising anadaptive interleaver 20, a transmitter 30, a transmission channel 35, areceiver/decoder 40 and a controller 50. The adaptive interleaver 20interleaves data that is transmitted by the transmitter 30 over thetransmission channel 35. The receiver/decoder 40 receives and decodesthe interleaved data. The controller 50 determines performanceparameters of the system in an effort to determine whether interleavingis beneficial and if it can be implemented. The controller alsogenerates an adaptive interleave control signal 58 in response to theperformance parameters. The adaptive interleaver preferably adjusts theinterleave depth in response to the adaptive interleave control signal58.

The adaptive interleaver 20 preferably comprises means for receiving amultiple bit adaptive interleave control signal and means for adjustingthe interleave depth in response to the adaptive interleave controlsignal as known to those skilled in the art. The adaptive interleaver 20preferably further comprises means for adaptively interleaving data atdifferent interleave depths as known to those skilled in the art. Theadaptive interleaver 20 is preferably coupled with the transmitter 30and the controller 50. The phrase “coupled with,” as used herein, meanscoupled either directly or indirectly via one or more interveningelements. One example of an adaptive interleaver is shown in U.S. Pat.No. 4,901,319 which is hereby incorporated by reference.

The adaptive interleaver 20 preferably receives data and interleaves thedata by rearranging the order in which the bits that comprise the dataare transmitted. The interleave depth is preferably defined as thedistance between bits that originally were adjacent to one another. Theinterleave depth is altered by varying the distance between originallyadjacent bits. The data is preferably encoded through the use of codingtechniques known to those skilled in the art before it is received bythe adaptive interleaver 20. Alternatively, any suitable adaptiveinterleaver that is responsive to a multiple bit adaptive interleavecontrol signal, as known to those skilled in the art, can be configuredfor use in the present embodiments.

The transmitter 30 preferably comprises an Asymmetric Digital SubscriberLine (ADSL) transmitter as known to those skilled in the art.Alternatively, the transmitter 30 can comprise a digital transmitter foruse with any form of transmission media as known to those skilled in theart. Alternatively, the transmitter 30 can comprise any transmitter foruse with any form of transmission media as known to those skilled in theart. The transmitter 30 is preferably coupled with the adaptiveinterleaver 20, the data rate monitor 60 and the transmission channel35.

The transmitter 30 modulates data for transmission to thereceiver/decoder 40 via the transmission channel 35 as known to thoseskilled in the art. The transmitter 30 can preferably transmit data atdifferent data rates as known to those skilled in the art. The capacityof the transmission channel 35 is one common factor that can be used asa basis for adjusting the data rate. The capacity of the transmissionchannel 35 typically depends on factors including the following: thedistance a transmission has to travel; the wire gauge of thetransmission channel; the number of bridged-taps on the transmissionchannel; the temperature of the transmission channel; the splice loss ofthe transmission channel; noise present in the transmission channel; andthe precision of the transmitter and receiver. While many of thesefactors are not directly measurable, their cumulative effect may bemonitored by measuring one or both of the SNR and BER of the system.Thus, the data rate can be adapted in response to the SNR or BER.

The transmitter 30 typically adapts the data rate by altering the timeallowed for the transmission of a symbol comprising a number of bits.Accordingly, a greater or lesser number of bits can be transmittedwithin a given time interval depending upon the alterations.Alternatively, the data rate can be altered by modulating a greater orlesser number of bits into each transmission. For example, increasingthe number of usable points in a Quadrature Amplitude Modulation (QAM)constellation results in the modulation of more bits in eachtransmission. When the data rate is increased through either of thesemethods, the SNR of the system is generally decreased. A decrease in theSNR generally results in an increase in the BER when the data rateincreases or is unchanged. Thus, to maintain a given BER, there is aupper limit for the data rate for a particular transmission channel.Accordingly, by monitoring the SNR and BER, the data rate can beadapted, through the use of the methods described above, to the maximumdata rate possible while maintaining an acceptable BER. The data ratecan be adapted once at system start-up, or continuously as known tothose skilled in the art.

The transmission channel 35 preferably comprises twisted-pair conductivewire as known to those skilled in the art. Alternatively, thetransmission channel can comprise coaxial cable, optical fiber,free-space laser, radio or any other type of transmission media as knownto those skilled in the art. The transmission channel 35 is preferablycoupled with the transmitter 30 and the receiver/decoder 40.

The receiver/decoder 40 preferably comprises an ADSL receiver, anadaptive de-interleaver and a sequential decoder as known to thoseskilled in the art. Alternatively, the receiver/decoder 40 can comprisea digital receiver/decoder for use with any type of transmission mediaas known to those skilled in the art. Alternatively, thereceiver/decoder 40 can comprise any type of receiver/decoder for usewith any type of transmission media as known to those skilled in theart. For example, the receiver/decoder 40 can employ a Reed Solomondecoder or any other suitable error correcting decoder as known to thoseskilled in the art. The receiver/decoder 40 is preferably coupled withthe transmission channel 35 and the signal to noise ratio monitor 70.

The receiver/decoder 40 receives and demodulates the data from thetransmitter 30. After demodulation, the receiver/decoder 40de-interleaves the data and utilizes decoding techniques known to thoseskilled in the art to detect and correct errors in the data. Forexample, the receiver/decoder 40 can analyze data including redundantbits that are generated by an encoder prior transmission, to determinewhether any data was corrupted and thus requires correction.

The controller 50 preferably comprises a data rate monitor 60, a signalto noise ratio monitor 70, means 54 for analyzing input signals andmeans 56 for providing an adaptive interleave control signal. The datarate monitor 60 preferably comprises a monitor for determining the datarate of the system 10 as known to those skilled in the art. The datarate monitor 60 is preferably coupled with the transmitter 30 and thecontroller 50. The data rate can be determined by counting the number ofbits, bytes, symbols, blocks, frames, cells, or packets sent per timeinterval as known to those skilled in the art. Alternatively, the datarate can be inferred from the frequency of the master clock signal usedby the transmitter or from the symbol rate detected by thereceiver/decoder 40 as known to those skilled in the art. Alternatively,for manually controlled systems, the value in the data register holdingthe data rate that is set by the operator can be directly accessed bythe data rate monitor 60 to determine the data rate. Alternatively, thedata rate can be determined through a variety of other techniques, andany suitable method for determining the data rate can be adapted for usein the presently preferred system. Averaging many measurements of thedata rate can be performed to improve the accuracy of the current datarate calculations as known to those skilled in the art.

The data rate monitor 60 determines the data rate and generates an inputsignal 68 that preferably varies as a function of the data rate.Alternatively, the input signal 68 can take many forms. The input signal68 can be based in-whole or in-part on the data rate. The input signal68 can be analog or digital and linear or non-linear as known to thoseskilled in the art. Alternatively, the input signal 68 can be binarysuch that input signal 68 is greater than or less than a threshold valuebased upon the data rate as known to those skilled in the art. The datarate monitor 60 preferably determines the data rate and continuouslygenerates the input signal 68. Alternatively, the data rate monitor 60can determine the data rate and generate the input signal 68 in asampled fashion on a random or non-random basis.

The signal to noise ratio monitor 70 preferably comprises a monitor fordetermining the SNR as known to those skilled in the art. The SNRmonitor 70 is preferably coupled with the transmission channel 35 andthe controller 50. SNR is preferably defined as the ratio of averagesignal power to average noise power. The signal power can be determinedby measuring the maximum amplitude and phase deviation of all receiveddata prior to demodulation. The noise power can be determined bymeasuring the amplitude and phase distance between adjacent points inthe modulation constellation as known to those skilled in the art.Alternatively, the SNR can be determined through a variety of othertechniques, and any suitable method of determining the SNR can beadapted for use in the presently preferred system. Averaging manymeasurements of SNR can be performed to improve the accuracy of thecurrent SNR calculations as known to those skilled in the art.

The signal to noise ratio monitor 70 preferably determines the SNR andgenerates an input signal 78 that varies as a function of the SNR.Alternatively, the input signal 78 can take many forms. The input signal78 can be based in-whole or in-part on the SNR. The input signal 78 canbe analog or digital and linear or non-linear as known to those skilledin the art. Alternatively, the input signal 78 can be binary such thatthe input signal 78 is greater than or less than a threshold value basedupon the SNR as known to those skilled in the art. The SNR monitor 70preferably determines the SNR and continuously generates the inputsignal 78. Alternatively, the SNR monitor 70 can determine the SNR andgenerate the input signal 78 in a sampled fashion on a random ornon-random basis.

The means 54 for analyzing input signals preferably comprises means fordetermining whether the current data rate satisfies a threshold, basedupon an analysis of the input signal 68. Alternatively, the means 54 foranalyzing input signals can comprise means for determining the currentdata rate based upon an analysis of the input signal 68. Alternatively,the means 54 for analyzing input signals can analyze both input signals68, 78. The means 54 for analyzing input signals is preferablyimplemented in computer readable program code written in any suitableprogramming language and implemented on an analog or a digital computerutilizing any suitable operating system. The means 54 for analyzinginput signals can also be implemented through the use of hardware in theform of a hardwired computer, an integrated circuit, or a combination ofhardware and computer readable program code.

The means 56 for providing an adaptive interleave control signalpreferably comprises means for providing the input signal 78 as it isreceived from the SNR monitor 70. Accordingly, the adaptive interleavecontrol signal 58 is preferably equivalent to the received input signal78. Alternatively, the adaptive interleave control signal 58 can takemany forms. The adaptive interleave control signal can be based in-wholeor in-part on one or both of the input signals 68, 78. The adaptiveinterleave control signal 58 can be analog or digital and linear ornon-linear as known to those skilled in the art. Alternatively, theadaptive interleave control signal 58 can be binary such that theadaptive interleave control signal produced is greater than or less thana threshold value based upon one or both of the input signals 68, 78 asknown to those skilled in the art. The means 56 for providing anadaptive interleave control signal is preferably implemented in computerreadable program code written in any suitable programming language andimplemented on an analog or a digital computer utilizing any suitableoperating system. The means 56 for providing an adaptive interleavecontrol signal can also be implemented through the use of hardware inthe form of a hardwired computer, an integrated circuit, or acombination of hardware and computer readable program code.

Referring now to FIG. 3, a transmission system 100 comprising theadaptive interleaver 20, the transmitter 30, the transmission channel35, the receiver/decoder 40 and a controller 150 according to analternate embodiment is shown. The adaptive interleaver 20, transmitter30, transmission channel 35 and receiver/decoder 40 are all the same asdescribed above.

The controller 150 preferably comprises a data rate monitor 60, a biterror rate monitor 170, means 154 for analyzing input signals and means156 for providing an adaptive interleave control signal. The data ratemonitor 60 is the same as described above. The bit error rate monitor170 preferably comprises a monitor for determining BER as known to thoseskilled in the art. The bit error rate monitor 170 is preferably coupledwith the receiver/decoder 40 and the controller 150. BER is preferablydefined as the relative frequency of error bits to received bits. TheBER is preferably determined though the use of a cyclic redundancy code(CRC) in the encoded symbols A CRC enables a bit error rate monitor todetermine when errors in the decoded symbols occur. By monitoring theerrors identified through the use of the CRC over a period of time, theBER of the system can be determined. Alternatively, BER can bedetermined through a variety of other techniques, and any suitablemethod of determining BER can be adapted for use in the presentlypreferred system. Averaging many measurements of BER can be performed toimprove the accuracy of the current BER calculations as known to thoseskilled in the art.

The bit error rate monitor 170 preferably generates an input signal 178that varies as a function of the BER. Alternatively, the input signal178 can take many forms. The input signal 178 can be based in-whole orin-part on the BER. The input signal 178 can be analog or digital andlinear or non-linear as known to those skilled in the art.Alternatively, the input signal 178 can be binary such that the inputsignal 178 is greater than or less than a threshold value based upon theBER as known to those skilled in the art. The BER monitor 170 preferablydetermines the BER and continuously generates the input signal 178.Alternatively, the BER monitor 170 can determine the BER and generatethe input signal 178 in a sampled fashion on a random or non-randombasis.

The means 154 for analyzing input signals preferably comprises means fordetermining whether the current data rate exceeds a predeterminedthreshold, based upon an analysis of the input signal 68. Alternatively,the means 154 for analyzing input signals can comprise means fordetermining the current data rate based upon an analysis of the inputsignal 68. Alternatively, the means 154 for analyzing input signals cananalyze both of the input signals 68, 178. The means 154 for analyzinginput signals is preferably implemented in computer readable programcode written in any suitable programming language and implemented on ananalog or a digital computer utilizing any suitable operating system.The means 154 for analyzing input signals can also be implementedthrough the use of hardware in the form of a hardwired computer, anintegrated circuit, or a combination of hardware and computer readableprogram code.

The means 156 for providing an adaptive interleave control signalpreferably comprises means for providing the input signal 178 as it isreceived from the BER monitor 170. Accordingly, the adaptive interleavecontrol signal 158 is preferably equivalent to the received input signal178. Alternatively, the adaptive interleave control signal 158 can takemany forms. The adaptive interleave control signal 158 can be basedin-whole or in-part on one or both of the input signals 68, 178. Theadaptive interleave control signal 158 can be analog or digital andlinear or non-linear as known to those skilled in the art.Alternatively, the adaptive interleave control signal 158 can be binarysuch that the adaptive interleave control signal 158 is greater than orless than a threshold value based upon one or both of the input signals68, 178 as known to those skilled in the art. The means 156 forproviding an adaptive interleave control signal in response to the inputsignals is preferably implemented in computer readable program codewritten in any suitable programming language and implemented on ananalog or a digital computer utilizing any suitable operating system.The means 156 for providing an adaptive interleave control signal inresponse to the input signals can also be implemented through the use ofhardware in the form of a hardwired computer, an integrated circuit, ora combination of hardware and computer readable program code.

While the controller 50, 150 and adaptive interleaver 20 are preferablyimplemented as separate elements as shown in FIGS. 1 and 2, they canalternatively be implemented as a single element comprising software,hardware or a combination thereof as described herein and known to thoseskilled in the art.

Referring now to FIG. 4, a transmission system 180 comprising theadaptive interleaver 20, the transmitter 30, the transmission channel35, the receiver/decoder 40 and a controller 80 is shown. The adaptiveinterleaver 20, transmitter 30, transmission channel 35 andreceiver/decoder 40 are all the same as described above. The controller80 preferably comprises a signal to noise ratio monitor 72 as describedherein. The signal to noise ratio monitor 72 generates a multiple bitadaptive interleave control signal 74 that preferably varies as afunction of the SNR. The adaptive interleave control signal 74 can bebased in-whole or in-part on the SNR. The adaptive interleave controlsignal 74 can be analog or digital and linear or non-linear as known tothose skilled in the art. Alternatively, the adaptive interleave controlsignal 74 can be binary such that the adaptive interleave control signalproduced is greater than or less than a threshold value based upon theSNR as known to those skilled in the art. The controller 80 ispreferably coupled with to the adaptive interleaver 20 such that theadaptive interleave control signal 74 is supplied directly to theadaptive interleaver 20. The adaptive interleave control signal 74 ispreferably utilized by the adaptive interleaver 20 to control theinterleave depth to generate an adaptively interleaved signal.

Referring now to FIG. 5, a transmission system 190 comprising theadaptive interleaver 20, the transmitter 30, the transmission channel35, the receiver/decoder 40 and a controller 90 is shown. The adaptiveinterleaver 20, transmitter 30, transmission channel 35 andreceiver/decoder 40 are all the same as described above. The controller90 preferably comprises a bit error rate monitor 172 as describedherein. The bit error rate monitor 172 generates a multiple bit adaptiveinterleave control signal 174 that preferably varies as a function ofthe BER. The adaptive interleave control signal 174 can be basedin-whole or in-part on the BER. The adaptive interleave control signal174 can be analog or digital and linear or non-linear as known to thoseskilled in the art. Alternatively, the adaptive interleave controlsignal 174 can be binary such that the adaptive interleave controlsignal produced is greater than or less than a threshold value basedupon the BER as known to those skilled in the art. The controller 90 ispreferably coupled with the adaptive interleaver 20 such that theadaptive interleave control signal 174 is supplied directly to theadaptive interleaver 20. The adaptive interleave control signal 174 ispreferably utilized by the adaptive interleaver 20 to control theinterleave depth to generate an adaptively interleaved signal.

Referring now to FIG. 6, a transmission system 200 comprising theadaptive interleaver 20, the transmitter 30, the transmission channel35, the receiver/decoder 40 and a controller 210 is shown. The adaptiveinterleaver 20, transmitter 30, transmission channel 35 andreceiver/decoder 40 are all the same as described above. The controller210 preferably comprises a data rate monitor 202 as described herein.The data rate monitor 202 generates a multiple bit adaptive interleavecontrol signal 204 that preferably varies as a function of the datarate. The adaptive interleave control signal 204 can be based in-wholeor in-part on the data rate. The adaptive interleave control signal 204can be analog or digital and linear or non-linear as known to thoseskilled in the art. Alternatively, the adaptive interleave controlsignal 204 can be binary such that the adaptive interleave controlsignal produced is greater than or less than a threshold value basedupon the data rate. The controller 210 is preferably coupled with theadaptive interleaver 20 such that the adaptive interleave control signal204 is supplied directly to the adaptive interleaver 20. The adaptiveinterleave control signal 204 is preferably utilized by the adaptiveinterleaver 20 to control the interleave depth to generate an adaptivelyinterleaved signal.

The system shown in FIG. 2 can be used to implement the method 300 shownin FIG. 7. The data rate monitor 60 determines the data rate (step 302,FIG. 7) of the transmission system 10. The data rate monitor 60generates an input signal 68 (step 304) that varies as a function of thedata rate. The signal to noise ratio monitor 70 determines a SNR (step306) of the system 10. The signal to noise ratio monitor 70 generates aninput signal 78 (step 308) that varies as a function of the SNR. Thecontroller 50 analyzes the first input signal 68 (step 310) anddetermines whether the data rate exceeds a predetermined threshold. Thecontroller 50 provides an adaptive interleave control signal 58 (step312) in response to the input signals 68, 78.

The system shown in FIG. 3 can be used to implement the method 320 shownin FIG. 8. The data rate monitor 60 determines the data rate (step 322,FIG. 8) of the transmission system 100. The data rate monitor 60generates a first input signal (step 324) that varies as a function ofthe data rate. The bit error rate monitor 170 determines a BER (step326) for the transmission system 100. The bit error rate monitor 170generates a second input signal (step 328) that varies as a function ofthe BER. The controller 150 analyzes the first input signal 68 (step330) and determines whether the data rate exceeds a predeterminedthreshold. The controller provides an adaptive interleave control signal(step 332) in response to the input signals 68, 178.

In a preferred embodiment, the predetermined threshold is determined inrelation to the data rate. When the data rate is above a certain level,the system cannot afford the decoder the additional time needed tode-interleave the interleaved data. Thus, for data rates above a certainlevel, interleaving imposes an unacceptable time delay on thetransmissions. Therefore, when the data rate exceeds the predeterminedthreshold, interleaving is preferably disabled. When the controller 50,150 determines that the data rate exceeds the predetermined threshold,the controller 50, 150 preferably generates an adaptive interleavecontrol signal 58, 158 (respectively) that controls the adaptiveinterleaver 20 such that no interleaving is implemented by the adaptiveinterleaver 20. Alternatively, when the data rate exceeds thepredetermined threshold, the controller 50, 150 can cease generating anadaptive interleave control signal such that no interleaving isimplemented by the adaptive interleaver 20. Thus, interleaving is onlyimplemented when the data rate is below a certain level.

Alternatively, if the data rate is below the predetermined threshold,the controller 50, 150 preferably generates an adaptive interleavecontrol signal 58, 158 that controls the adaptive interleaver 20 suchthat interleaving is implemented. The adaptive interleave control signal58, 158 preferably causes the adaptive interleaver 20 to implement aninterleave depth that is proportional to the SNR, BER, data rate orcombination thereof. Alternatively, the interleave depth can beinversely proportional to the SNR, BER, data rate or combinationthereof. Alternatively, the adaptive interleave control signal 58, 158can cause the adaptive interleaver 20 to implement a number of differentinterleave depths depending upon the SNR, BER, data rate or combinationthereof. For example, the controller 50, 150 can implement fivedifferent graduated interleave depths in response to the SNR or BER,assuming that the data rate is high enough to allow for suchinterleaving. Each of the different graduated interleave depths isimplemented when the SNR or BER is within a predetermined range ofvalues.

The system of FIG. 4 can be used to implement the method 340 of FIG. 9.The signal to noise ratio monitor 72 determines a SNR (step 342) of thetransmission system 180. The signal to noise ratio monitor 72 generatesan adaptive interleave control signal 74 (step 344) that preferablyvaries as a function of the SNR. The adaptive interleaver 20 receivesthe adaptive interleave control signal and preferably adapts aninterleave depth in response to the adaptive interleave control signal74.

The system of FIG. 5 can be used to implement the method 350 of FIG. 10.The bit error rate monitor 172 determines a BER (step 352) of thetransmission system 190. The bit error rate monitor 172 generates anadaptive interleave control signal 174 (step 354) that preferably variesas a function of the BER. The adaptive interleaver 20 receives theadaptive interleave control signal preferably adapts an interleave depthin response to the adaptive interleave control signal 174.

The system of FIG. 6 can be used to implement the method 360 of FIG. 11.The data rate monitor 202 determines a data rate (step 362) of thesystem 200. The data rate monitor 202 generates an adaptive interleavecontrol signal 204 (step 364) that preferably varies as a function ofthe data rate. The adaptive interleaver 20 receives the adaptiveinterleave control signal and preferably adapts an interleave depth inresponse to the adaptive interleave control signal 204.

It is to be understood that during operation, the interleave depthimplemented by the adaptive interleaver 20 (FIGS. 2, 3, 4, 5 and 6) isgenerally communicated to the receiver/decoder 40 at the other end ofthe transmission channel 35 as known to those skilled in the art. If theinterleave depth is adjusted solely as a function of the data rate, boththe adaptive interleaver 20 and the receiver/decoder 40 can monitor thecurrent data rate, and can synchronize the interleaving depth throughthe use of the same interleave depth control rules as known to thoseskilled in the art. However, if the SNR or the BER is used to determinethe interleave depth, additional mechanisms can be used to assure thatthe interleave depth implemented by the adaptive interleaver 20 matchesthe interleave depth of a de-interleaver during the decoding process asknown to those skilled in the art. Accordingly, the current interleavedepth being used by the adaptive interleaver 20 can be transmitted tothe receiver/decoder 40 for use in the decoding process. The componentsand methods required to perform such a transmission and synchronize theencoding and decoding processes are well known to those skilled in theart.

It is to be understood that a wide range of changes and modifications tothe embodiments described above will be apparent to those skilled in theart and are contemplated. It is therefore intended that the foregoingdetailed description be regarded as illustrative rather than limiting,and that it be understood that it is the following claims, including allequivalents, that are intended to define the spirit and scope of theinvention.

1. A controller for an adaptive interleaver comprising: a processor thatis operative to determine a signal to noise ratio of a transmissionchannel, determine a data rate of the transmission channel, analyze thesignal to noise ratio, analyze the data rate, and generate a controlsignal.
 2. The invention of claim 1, wherein the processor is furtheroperative determine a signal power by measuring a maximum amplitudedeviation and a maximum phase deviation of data received via thetransmission channel.
 3. The invention of claim 1, wherein the processoris further operative determine a noise power by measuring an amplitudedistance and a phase distance between adjacent points in a modulationconstellation.
 4. The invention of claim 1, wherein the processor isfurther operative to determine whether the signal to noise ratio exceedsa threshold.
 5. The invention of claim 1, wherein the processor isfurther operative to determine whether the data rate exceeds athreshold.
 6. The invention of claim 1, further comprising an adaptiveinterleaver coupled with the processor, the adaptive interleaver beingoperative to receive the control signal.
 7. The invention of claim 6,wherein the adaptive interleaver is operative to alter an interleavedsignal in response to the control signal.
 8. The invention of claim 6,wherein the adaptive interleaver is operative to alter the interleavedepth of an interleaved signal in response to the control signal.